Brother HL 1240 - B/W Laser Printer Service Manual page 135

I-2 Dark
(1) Check the paper used meets the recommended paper specifications.
(2) Check the printer's environment. High temperature and high humidity conditions
can increase the amount of background shading.
(3) Clean the corona wire with the wire cleaner.
(4) Try installing a new toner cartridge or drum unit.
Possible cause Step
Corona failure 1
(contact failure)
Drum unit failure 2
Toner cartridge 3
failure
High-voltage 4
power supply
PCB failure
Main PCB failure 5
Engine PCB 6
failure
User Check
Check
Are the charge electrodes
between the printer body and
the drum unit dirty?
Is the problem solved after
replacing the drum unit?
Is the problem solved after
replacing the toner cartridge?
Is the connections of the
connector between the high-
voltage power supply PCB and
the engine PCB secured
correctly?
Are there any disconnected
connectors?
Are there any disconnected
connectors?
Result
Yes
Yes
Yes
Yes
No
No
6-25
CHAPTER 6 TROUBLESHOOTING
Remedy
Clean both electrodes.
Replace the drum unit
with a new one.
Replace the toner
cartridge with a new
one.
Replace the high-
voltage power supply
PCB.
Replace the main
PCB.
Replace the engine
PCB.
Ground
contacts